Exciton footprint of self-assembled AlGaAs quantum dots in core-shell nanowires

Fontana, Yannik; Corfdir, Pierre; Hattem, B. Van; Russo-Averchi, Eleonora; Heiß, Martin; Sonderegger, Samuel; Magén, Cesar; Arbiol, Jordi; Phillips, R. T.; Morral, Anna Fontcuberta i

doi:10.1103/physrevb.90.075307

Cited by 21 publications

(25 citation statements)

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“…The nanowire geometry together with the contrast between the dielectric constant of the nanowire and its surroundings lead to a polarization anisotropy in absorption and emission [1]. This nanowire antenna effect has been observed for nanowires with a diameter ϕ much smaller as well as on the order of the wavelength λ of the nanowire's luminescence [1][2][3][4][5][6][7][8]. In the former case, the antenna effect can be understood by simple electrostatic considerations [1], whereas it is caused by the coupling of light into the guided modes supported by the nanowire for the latter case [3].…”

Section: Introductionmentioning

confidence: 97%

Importance of the dielectric contrast for the polarization of excitonic transitions in single GaN nanowires

et al. 2015

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We investigate the polarization of excitonic transitions of single dispersed GaN nanowires with a diameter of about 50 nm. We observe donor-bound exciton transitions with a linewidth narrower than 250 μeV at 10 K, whereas the luminescence from free excitons exhibits a width of up to 5 meV. This broadening is larger than that observed for free excitons in the as-grown nanowire ensemble and is the result of inhomogeneous strain introduced by the nanowire dispersion. This strain lowers the symmetry of the lattice structure and allows A excitons to emit light polarized parallel to the nanowire axis. The polarization anisotropy of A excitons, however, is found to largely vary from one nanowire to another. In addition, the various bound-exciton lines in a given nanowire do not show the same polarization anisotropies. These findings can be explained by the dielectric contrast between the nanowire and its environment, but only when taking into account the strong variations of the dielectric function of GaN at the near band-edge.

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Section: Introductionmentioning

confidence: 97%

Importance of the dielectric contrast for the polarization of excitonic transitions in single GaN nanowires

et al. 2015

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“…Emerging peaks around 1.814 eV and 1.817 eV correspond, respectively, to the biexciton (broadened by its sideband 46 ) and the second charged exciton. 34 The histogram of the QD single exciton transition energies issued by the analysis of the same batch of nanowires used for APT is shown in Fig. 4(b).…”

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confidence: 99%

“…27 Previous studies of these structures performed by highresolution scanning transmission electron microscopy (HR-STEM), electron energy loss spectroscopy (EELS), and energy-dispersive X-ray spectroscopy (EDX) indicated that QDs may form at the outer corner of the hexagon in the AlGaAs shell, at the termination of an Al-segregation region. 27,34 However, it was not possible to fully characterize the shape of the dots nor ascertain whether other mechanisms of QD formation may occur within the AlGaAs shell. In addition, the elemental contrast in TEM techniques is limited by the thickness of the slab and by the density contrast of the nanostructure.…”

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confidence: 99%

Three-dimensional nanoscale study of Al segregation and quantum dot formation in GaAs/AlGaAs core-shell nanowires

Mancini

Fontana

Conesa‐Boj

et al. 2014

Applied Physics Letters

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GaAs/Al-GaAs core-shell nanowires fabricated by molecular beam epitaxy contain quantum confining structures susceptible of producing narrow photoluminescence (PL) and single photons. The nanoscale chemical mapping of these structures is analyzed in 3D by atom probe tomography (APT). The study allows us to confirm that Al atoms tend to segregate within the AlGaAs shells towards the vertices of the hexagons defining the nanowire cross section. We also find strong alloy fluctuations remaining AlGaAs shell, leading occasionally to the formation of quantum dots (QDs). The PL emission energies predicted in the framework of a 3D effective mass model for a QD analyzed by APT and the PL spectra measured on other nanowires from the same growth batch are consistent within the experimental uncertainties. V C 2014 AIP Publishing LLC.[http://dx.doi.org/10.1063/1.4904952] Epitaxial semiconductor quantum dots (QDs) have been extensively studied over the last three decades because of their peculiar optical properties such as narrow luminescence and single photon emission. The structure and chemical composition of QDs has traditionally been assessed by scanning tunneling microscopy (STM) or transmission electron microscopy (TEM) related techniques. 1 In the last decade, laser-assisted atom probe tomography (LA-APT) 2 has emerged as a tool for the determination of the morphology and of the chemical composition of nanoscale semiconductor heterostructures with sub-nanometer resolution in 3D. 3,4 In the past few years, several APT-based studies addressed a limited number of QD structures. 4-10 Quantum dots can be inserted in semiconductor nanowires either deterministically, with specific shape and composition, 11-14 or as self-assembled structures. [15][16][17][18] Nanowires, furthermore, represent a model system for atom probe analysis, 19-24 as they closely approximate the shape of a field-emission tip. Nevertheless, and despite the interest of nanowire-based QDs for quantum information [25][26][27][28][29] and for their integration in nanoscale optoelectronic devices, [30][31][32][33] no studies of nanowire QDs by APT have been reported yet.Core-shell GaAs/AlGaAs nanowires grown by molecular beam epitaxy (MBE) have been shown to exhibit narrow luminescence and single photon emission, ascribed to QDs forming occasionally at the external corners of the AlGaAs shells. 27 Isolated emissions centered around 670 nm ($1.85 eV) could be found by cathodoluminescence (CL) spectroscopy, with a typical mean frequency along the axis of the order of one spot per micron. 27 Previous studies of these structures performed by highresolution scanning transmission electron microscopy (HR-STEM), electron energy loss spectroscopy (EELS), and energy-dispersive X-ray spectroscopy (EDX) indicated that QDs may form at the outer corner of the hexagon in the AlGaAs shell, at the termination of an Al-segregation region. 27,34 However, it was not possible to fully characterize the shape of the dots nor ascertain whether other mechanisms of QD formation may occ...

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“…Several high-resolution imaging methods have demonstrated that the Al x Ga 1Àx As shells are indeed not homogeneous and contain nanoscale Ga-rich islands. [20][21][22] Another explanation for the peculiar peaks in the emission spectrum from the Al x Ga 1Àx As shell has been proposed, where the luminescence could originate from recombination at lattice point defects. 23 If this would be the case, one would expect that the QD emission would be proportional to the Al x Ga 1Àx As shell volume and mainly independent of the NW crosssection morphology.…”

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confidence: 99%

“…The observed QD density as a function of the shell thickness confirms that the nature of the QD emission does not originate from atom-sized point-like defects but from segregations either at the corners or at the facets of the Al x Ga 1Àx As shells as recently shown by high-resolution TEM and atom probe tomography studies. [20][21][22] …”

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confidence: 99%

Quantum dots in the GaAs/AlxGa1−xAs core-shell nanowires: Statistical occurrence as a function of the shell thickness

Francaviglia

Fontana

Conesa‐Boj

et al. 2015

Applied Physics Letters

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Quantum dots (QDs) embedded in nanowires represent one of the most promising technologies for applications in quantum photonics. Self-assembled bottom-up fabrication is attractive to overcome the technological challenges involved in a top-down approach, but it needs post-growth investigations in order to understand the self-organization process. We investigate the QD formation by selfsegregation in Al x Ga 1Àx As shells as a function of thickness and cross-section morphology. By analysing light emission from several hundreds of emitters, we find that there is a certain thickness threshold for the observation of the QDs. The threshold becomes smaller if a thin AlAs layer is pre-deposited between the GaAs nanowire core and the Al x Ga 1Àx As shell. Our results evidence the development of the quantum emitters during the shell growth and provide more guidance for their use in quantum photonics. V C 2015 AIP Publishing LLC. [http://dx

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Exciton footprint of self-assembled AlGaAs quantum dots in core-shell nanowires

Cited by 21 publications

References 61 publications

Importance of the dielectric contrast for the polarization of excitonic transitions in single GaN nanowires

Importance of the dielectric contrast for the polarization of excitonic transitions in single GaN nanowires

Three-dimensional nanoscale study of Al segregation and quantum dot formation in GaAs/AlGaAs core-shell nanowires

Quantum dots in the GaAs/AlxGa1−xAs core-shell nanowires: Statistical occurrence as a function of the shell thickness

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